Zinc alloy



pecially adapted for the production of stereotype type plates and to fill the detailed design of the lead alloys in other fields in which die casting Patented Jan. 29, 1935 ZINC ALLOY William Waite Broughton, Hohokus, N. J., and George L. Werley, Palmer-ton, Pa., assignors to The New Jersey Zinc Company, New York, N. Y., a corporation of New Jersey No Drawing. Application April 18, 1934, Serial No. 721,152

4 Claims. (Cl. 751) ing freezing create the following dilemma when zinc alloys of the prior art are used:

(.a) If the mold is fully lined by the use of a paper insert in the back of the mold in addition to the paper matrix in the face of the mold, in order to secure uniform cooling of the casting, the cooling rate will be too slow on account of the insulating action of the matrix and insert, so that the matrix and insert will be in part consumed by the heat and the gases thereby evolved will cause severepitting.

(b) If the paper insert is omitted and the back of the mold left'bare tm-secure sufliciently rapid cooling to protect the paper matrix from over-heating, the differential cooling will cause freezing to begin at therelatively cool back of the mold and the shrinkage of the metal during freezing will tend to draw the metal locally away from the matrix, so that the surface of the final cast plate will be marred by shrinkage depressions.

We have now discovered a zinc base alloy which possesses the properties requisite for the successful die casting of stereotype plate.

The new zinc base alloy contains aluminum and copper in such proportions that sufficient eutectic is present to insure freezing over a narrow temperature range. The alloy should not contain more than 0.05% lead, and preferably not more than 0.01% lead; in consequence, zinc of high purity should be used in compound- The present invention relates to zinc alloys and has for its object the provision of an improved zinc base alloy. More particularly, the invention aims to provide an improved zinc base alloy esplates by die casting.

Stereotype plates have heretofore been made of antimonial lead or lead-antimony-tin alloys. The plates are cast in a mold containing a paper matrix, which lines one face of the mold cavity. The paper matrix contains the design to be reproduced on the stereotype plate. The metal may be poured into these molds by hand with a ladle or it may be poured into the molds by machines similar to die casting machines or to the machines used in type casting.

The usual lead alloys used in the preparation of stereotype plates have numerous disadvantages. Among these may be mentioned great weight (a specific gravity of about 11 as com pared with a value of 6.7 for the zinc alloy of the present invention), softness, lack of impact strength, and lack of ductility. On account of the last mentioned defect, stereotype plates intended for use on the cylinders of rotary presses must be cast curved to fit the cylinder, since the metal cannot ordinarily be bent to fit the cylinder after casting withoutcracking.

In spite of the recent great development of the use of zinc base alloys in the die casting industry, no zinc base die casting alloy has heretomg the alloyfore been developed that could be substituted for 1 The composltlon of t alloy may be as ows:

lead alloys in the production of stereotype plates,

though zinc base alloys have largely displaced Aluminum to preferably to 5.85%, copper 0.3 to 1.8%, preferably 0.85 to 1.35% and the balance zinc of high purity, preferably containing-not'more than 0.01% lead.

If the copper content of the alloy exceeds 1.8%, the aluminum content must be appropriately increased to insure the presence of suiiicient euis appropriate. I

The zinc base die casting alloys of the prior art have proven to be unsuitable for the production of stereotype plates largely for one or all of the following reasons:

1. They have a tendency to crack when cast in thin plates of irregular thickness.

2. They lack suflicient fluidity to flow through the thin mold cavity requisite for casting stereomay advantageously exceed the copper percentage by about 5. It will be understood that the melting point of such alloys with copper content exceeding 1.8% is greater than the melting point of the alloys within the preferred'ranges given Paper matrix, particularly the dots used 111 half above and that allowance for this increased tone reproductionfimelting point must be made in the use of the 3. The relatively high melting point of zincalloy,

base die casting alloys and their shrinkage dur The alloys of the invention are not only partectic; for example, thealuminum percentage ticularly suitable for die casting stereotype plates 11 it also for other thin articles, for example medallions, tokens, and the like. Plates 0.097 inch thick (that is to say, 7 points high, in printers terminology) can be readily die cast with these alloys without cracking. Furthermore,

Analysis Lead alloy Zinc alloy a egg, alu num L g;

n lmony nnpnr Tin 5.69: Balance zinc (99.99%pure Physical properties Lead alloy Zinc alloy Tensile strength-lbJsq. in 8,400. 43,600. Impact strength-it. lbs .25 (f' sq. 19.00 04" sq.

- specimens) specimens). Brinell hardnm 17 87 Percent elongation in 2" .5- 3.7

Using the standard practice of applying a 500 kg. load on a 10 mm. ball for 30 seconds, the average diameter of impressions for the lead alloy was 5.8 mm., whereas the average diameter for the zinc alloy was only 2.7 mm.

The alloys of the invention are substantially lighter than the antimonial lead or'antimonylead-tin alloys commonly used in casting stereo-- type plates. The specific gravity of these lead alloys is approximately 11; that'of the zinc alloys in accordance with the present invention is about 6.7.. Thus, plates die cast of zinc base alloys weigh only about 61% as much as stereotype platesof the same size castgwith the conventional lead alloys. Further substantial economy can .sufliciently low to avoid crushing the type of aluminum, 0.3 to 1.8% copper, and the balance be obtained by casting zinc base alloy plates thinner than is customary with lead alloys. For

example, plates cast with a zinc alloy 01. the invention 0.097 inch thick will be mechanically stronger than plates 0.25 inch thick cast with the usual lead stereotype alloys. Thus, the impact strength of a test-bar, measuring 0.25 inch by 0.35 inch, of ordinary lead-antimony-tin stereotype metal is about A foot pound; while a testbar, measuring 0.25 inch by 0.097 inch, of a zinc alloy of the invention has an impact strength exceeding- 6 foot pounds. v

In die casting stereotype plates with the zinc alloys of the invention, the pressure should be.

mat used. In the case of paper matspressures of 35 lbs. per square inch to 150 lbs. per square inch on the metal are appropriate. Either air type or plunger type die casting machines can be used in 'casting plates with the newalloys. The temperature of the molten zinc alloy during the casting operation may advantageously be maintained at between 415 and 450 C., preferably at about-427 C. a

We claim:

1. A zinc base alloy containing aluminum and copper in such proportions that suflicient of a eutectic is present to insure freezing over a narrow temperature range, the percentage of copper present being from .3- to 1.8, the percentage of aluminum exceeding the percentage of copper by about 5, and the balance being zinc metal containing not more than 0.05% lead.

2. A zinc base alloy consisting of 5.1 to 6.5%

zinc containing not more than'='0.05% lead.

a. A zinc base alloy consisting of 5.45 to 5.85% aluminum, 0.85 to 1.35 copper, and the balance zinc of high purity containing not more than 0.01% lead.

4. A cast metal object made of a zinc base alloy having a tensile strength above 40,000 pounds per square inch, containing 5.1 to 6.5% aluminum, 0.3 to 1.8% copper, the remainder being zinc the aluminum and copper being present in such proportions that suflicient of a eutectic is present to insure freezing over a narrow temperature range, and in which the zinc base is zinc metal containing not more than 0.05% lead.

WILLIAM WAITE BROUGHTON. GEORGE L. WERLEY.

CERTIFICATE or CORRECTION.

.Pate F N 1,989,308. Y .January 29, 1935.

WlLLlAM WAfITE BROUGHTON, ET AL.

It is hereby certified that error appears in the printed specification ol the above numbered patent requiring correctionas follows: Page 2; second column,

line'8, for "0.35" read 0.25; and that the said Letters Patent should be rea with this correction therein that the same mayconform to the record of the. a

case in the Patent Office. Signed and sealed this 12th day of March, A I). 1935.

Leslie F razer" Acting Commissioner of Patents. 

